1. Field of the Invention
This invention relates generally to dished reflector structures and more particularly concerns a lightweight foldable parabolic reflector and a radio frequency antenna assembly incorporating the foldable reflector.
2. State of the Prior Art
Parabolic and spherical reflectors are known and have been used in the field of communications for transmission and reception of radio signals, such as in microwave communication links, space communications and radio telescopes. Such reflectors have also found application outside the communication areas, as, for example, in the solar energy field, where they are used to collect and concentrate solar radiation.
In the past, dished reflectors of significant diameter, e.g., 10 to 15 feet, have been heavy and unwieldy assemblies and very costly and inconvenient to transport and install. This was due to the requirement of a high level of accuracy in the curvature of the reflector dish in order to obtain high signal gain and to avoid signal phasing problems at the focal point of the dish. In the past, these considerations have generally required rigid reflector structures to achieve and retain precise curvatures.
In isolated instances it was found necessary to design parabolic or otherwise curved reflectors of folding construction, such that a reflector may be folded into a compact assembly for transportation and then deployed for use. Notably, such folding reflectors have found application in the space communications field, where space vehicles require relatively large antennas which are folded during launch within the limited space available, and are then deployed outside the earth's atmosphere.
The folding reflector structures of the known prior art have typically included a reflecting mesh supported by a skeleton framework of radial arms pivotally mounted to a central hub. The radial arms were manufactured to the desired curvature of the reflector dish and were constructed to rigidly retain this curvature. These reflectors are deployed by simply pivoting the radial arms from a generally axial folded position to a generally radial extended or deployed position without any change in the pre-formed curvature of the radial arm. Such precisely curved, pre-formed arms are very expensive to manufacture and become impractical for larger diameter dishes.
The prior art known to the applicant in connection with deployable dish strucures is as follows:
Paper No. 100, authored by Lo f and Fester, presented at the United Nations Conference on New Sources of Energy, held in Rome in Aug., 1971.
The Conference proceedings concerning the area of solar energy for heating purposes, originally entitled Volume 5, Solar Energy II, has been republished by Cloudburst Press of America, Inc., 2116 Western Avenue, Seattle, Wash. 98121. The title of the republished volume is unknown, but is identified as: ISBN 0-88930-031-3 (soft cover); ISBN 0-88930-032-1 (hard cover).
The referenced paper No. 100 is found at pages 262 through 264 of this republished volume. The deployable solar cooker disclosed in this paper does not teach the present invention in that it relies only on the curvature of the pre-formed dish of reflecting fabric. As described the radial spokes are of spring metal and "flex only as forced by the fabric."
Man's Greatest Adventure by Laurence Allen, 1974, Library of Congress Card No. 74-17235, includes various photographs showing deployable antennas used on the lunar space mission. In particular, a small portable folded S-band dish antenna is shown at page 46. The S-band antenna photographs do not teach a folding stressed dish structure such as disclosed herein.
The ARRL Antenna Handbook, 1980, published by the American Relay League, shows at pages 254 and 255 a 12-foot stressed parabolic dish antenna. This structure is not deployable and radial spokes are stressed by guy wires attached to the focus feed support boom. The perimeter wire of the reference serves only as a peripheral support means for attaching nonelastic wire mesh segments to the rib skeleton to form a reflector surface.
It is contemplated by this reference that the dish be made portable by first removing the wire mesh, and then disassembling the rib structure.